feat: Embedded Documents (a.k.a Subdocuments)

[AlexStormwood]

This feature mostly already exists in v0.4.4. This issue is for tracking progress for this feature in the TypeScript rewrite of this package.

Tests to confirm this feature should be:

Golden Path Tests

• An Embedded Document should successfully create data per the Embedded Document's structure, where all data provided to create the document and its embedded documents are valid.
• An Embedded Document should successfully create data per the Embedded Document's structure, where any field that was not provided a value but has a default rule should create with the default data.
• An Embedded Document should successfully create data per the Embedded Document's structure, where a field that has a type of another Document should store only the Document ID in its database entry.
• An Embedded Document that inherits from another Embedded Document-based class should adhere to all fields/rules/constraints/etc defined in the parent class.
• An Embedded Document that inherits from another Embedded Document-based class should be able to override all fields/rules/constraints/etc defined in the parent class.

Error-Handling Tests

• An Embedded Document should throw an error when creating data where the Embedded Document fields are not meeting their defined required constraint.
• An Embedded Document should throw an error when creating data where the Embedded Document fields are not meeting their defined unique constraint.
• An Embedded Document should throw an error when creating data where the Embedded Document fields are not meeting their defined type constraint.
• An Embedded Document should throw an error when creating data where the Embedded Document fields are not meeting their defined min constraint.
• An Embedded Document should throw an error when creating data where the Embedded Document fields are not meeting their defined max constraint.
• An Embedded Document should throw an error when creating data where the Embedded Document fields are not meeting their defined choices constraint.
• An Embedded Document should throw an error when creating data where the Embedded Document fields are not meeting their defined validate constraint.

[AlexStormwood]

Not sure that this is needed, given that all EmbeddedDocument and Document functionality both stem from BaseDocument - and the Document tests are passing perfectly fine.